Iron compounds, including iron sulfide can form within pipeline networks that transport gas, oil, water and mixtures of gas, oil and water. The iron sulfide compounds are physically characterized as appearing to be amorphous solid particles capable of absorbing water and oil.
Hydrogen sulfide, H2S, is a naturally occurring contaminant of fluids that is encountered in many industries, including the oil and gas industry and the paper industry. The corrosive nature of H2S causes the accumulation of particulate iron sulfide. Iron sulfide becomes entrained in hydrocarbons, glycol, salts, and the like to form deposits on the surfaces of conduits such as pipelines. Such deposits present a significant problem because the deposits hinder accurate determinations of pipeline structural integrity and the pipelines must be cleaned physically.
Given the various chemical and physical conditions that go into the forming of iron sulfide several forms can be found in a given section of pipeline. It is seldom that a single type of iron sulfide exists but more generally it is a mixture of iron sulfide with mackinawite being the most dominant species present. Other species of iron sulfide commonly found in pipeline networks include: marcasite, pyrite, pyrrhotite, troilite and magnetite. The chemical formula for iron sulfide is commonly shown as FeS, which is the chemical formula for troilite. However depending upon the degree of oxidation and exposure to hydrogen sulfide gas, oxygen and other various physical elements it can include: Fe9S8 (mackinawite), FeS2 (Marcasite), FeS2 (Pyrite), Fe7S8 (Pyrrhotite).
The iron sulfide particles can adhere to the internal surfaces of pipeline networks and associated process equipment. The physical characteristic of the iron sulfide deposits can vary from a viscous, oil coated mass to a dry black powder form. The buildup of iron and iron sulfide deposits over time can lead to a range of operational problems. The presence of iron and iron sulfide deposits can lead to increased corrosion rates within pipeline networks. It can also lead to interference in the safe operation of pipeline valving systems, potentially leading to catastrophic system failures. Therefore, the cleaning of pipeline networks containing iron and iron sulfide deposits is a common practice within the pipeline industry.
In the oil industry, these ferrous deposits are a major source of economic loss. The deposits obstruct the flow of oil in wells, in the adjacent strata and in pipelines as well as in processing and refinery plants. Further such deposits tend to stabilize oil-water emulsions that tend to form during secondary oil recovery. Generally, the deposits present major problems to oil producers.
Many different methods for cleaning pipeline networks have developed over time. The cleaning methods used to decrease and remove the iron and iron sulfide deposits include mechanical pigging, batch chemical cleaning, and continuous chemical cleaning. The chemical compounds used in batch and in continuous cleaning methods includes chemicals based totally or in part upon: surfactants, solvents, acids, bases, oxidizing agents, chelating agents and combinations of these.
Using a strong acid is the simplest way to dissolve such a deposit. But using a strong acid generates large volumes of highly toxic H2S gas, which is an undesirable by-product. Using an oxidizing agent may avoid such toxicity hazards but produces oxidation products, including elemental sulphur which is corrosive to pipes. Another agent for treating such deposits is acrolein, but it also has health, safety and environmental problems.
It has been found that tris(hydroxymethyl)phosphine (referred to herein as THP and may be referred to elsewhere as THP or TRIS) is capable of solubilizing iron and iron sulfide by forming a THP Iron Ammonium complex that is water soluble. The water soluble THP Iron Ammonium complex is characteristically a red liquid solution. The THP is believed to be formed from the addition of Tetrakis(hydroxymethyl)phosphonium salts (referred to herein as THPS or THP Salts) especially the sulfate salt. THPS is commonly used as a flame retardant for textiles and also is added to oil wells, gas pipelines and water injection systems to reduce the interference of iron and iron sulfide. THPS is also recognized as an effective chemical to control the presence of sulfate reducing bacteria (referred to herein as SRB) and is regularly supplied as a biocide. A biocide is a chemical substance capable of killing living organisms, usually in a selective way. Biocides are commonly used in medicine, agriculture, forestry, and in where they prevent the fouling of water and oil pipelines. The presence of SRBs in part causes the presence of iron sulfide compounds in pipeline networks. It has been found that the effectiveness of THP salts in the removal of iron and iron sulfide compounds is not always at acceptable levels. This is believed to be due to the inconsistent composition of the iron and iron sulfide compounds as they exist within the pipe networks along with the ability to properly distribute the THP salts within the pipeline network.
Thus, tris(hydroxymethyl)phosphine (THP) is capable of solubilizing iron sulfide by forming a bright red water-soluble complex. THP is formed in oil wells treated with tetrakis(hydroxmethyl)phosphonium salts (THPS). THPS is commonly added to oil wells as a biocide to kill the sulfate reducing bacteria. Unfortunately, the effectiveness of THP as a solubilizing agent for iron sulfide varies considerably from well to well because the complex with iron sulfide requires the presence of ammonium ions. The concentration of ammonium ions in oil field water is frequently less than the optimum for iron sulfide removal. THP and THPS have stability problems at higher pH values. The use of THP with ammonia is hindered by the tendency of THP and ammonia to react together to form an insoluble polymer. The formulation of THP and ammonia is only fully stable at a pH below 4, and polymerization is rapid at any pH greater than 6, but the complex only forms readily at a pH above 5. If the ammonia concentration is high there is a risk of polymer depositing in the formation and obstructing the flow of oil or water. For all the foregoing reasons it is difficult to obtain consistent performance in preventing or removing iron sulphide scale using THP.
Phosphines are a class of compounds. Phosphines are alkyl or aryl derivatives of phosphine, just as amines can be regarded as derivatives of ammonia. Common examples include triphenylphosphine ((C6H5)3P) and BINAP, both used as phosphine ligands in metal complexes such as Wilkinson's catalyst. Metal phosphine complexes are catalysts for reactions such as the Sonogashira coupling. Most of these phosphines, with the exception of triphenyl phosphine, are made from pressurized, purified phosphine gas. A large industrial application of phosphine is found in the production of tetrakis(hydroxymethyl)phosphonium salts, made by passing phosphine gas through a solution of formaldehyde and a mineral acid such as hydrochloric acid. These salts find application as flame retardants for textile (Proban®—registered trademark of Rhodia UK Limited) and as biocides.
In a paper published in the Royal Society of Chemistry in 2000, entitled: “Self assembly of a novel water soluble iron (II) macrocyclic phosphine complex from tetrakis(hydroxymethyl)phosphonium sulfate and iron (II) ammonium sulfate: single crystal X-ray structure of the complex,” authors, John C. Jeffery, Barbara Odell, Nicola Stevens and Robert Talbot describe the mechanism by which a water soluble transition metal complex is formed. This paper was accepted for publication on Dec. 6, 1999. In this paper, the authors describe a series of reactions that lead to a situation where THPS aids in the dissolution of iron sulfide in oil fields leading to a red coloration of the treated water. The authors describe how the speciation of the iron sulfide (FeS) system in natural environments, such as oil wells, is necessarily complex. Further, their model reactions allow us to tentatively propose THPS and ammonia (NH4+) ions self assemble iron complexes where the iron originates from iron sulfide formed in oil wells owing to sulfate reducing bacteria or indigenous H2S.
A paper presented in 1998 in Mexico City referenced the use of THPS as an iron-sulfide dissolving agent. “Tetrakis(hydroxymethyl)phosphonium sulfate (THPS), A New Oilfield Bactericide Providing Iron Sulfide Dissolution and Environmental Benefits,” was presented by T. Haack, R. Diaz and R. E. Talbot, at Exitep 98, Mexico City, 15-16 November, 1998. In this paper, the authors noted in actual field conditions the use of THPS as a bactericide in pipelines also demonstrated the reduction in iron sulfide deposits. Therefore, it has been well established by those skilled in the art that THPS with ammonium salts is effective at dissolving iron sulfide deposits.
A feature of the present invention is to provide a composition for removing iron and iron sulfide solids from within pipeline networks.
Another feature of the present invention is to provide a composition that forms a water-soluble complex with the iron and iron sulfide solids.
Another feature of the present invention is to provide a composition for removing iron and iron sulfide solids in either batch or continuous applications.
A feature of the present invention is to provide a method for removing iron and iron sulfide solids from within pipeline networks.
Another feature of the present invention is to provide a method that forms a water-soluble complex with the iron and iron sulfide solids.
Another feature of the present invention is to provide a method for removing iron and iron sulfide solids in either batch or continuous applications.
A feature of the present invention is to provide a composition and method for forming a water-soluble complex with the iron and iron sulfide solids.
Another feature of the present invention is to provide a composition and method for removing iron and iron sulfide solids using a unique blend of metal complexing agents.
Yet another feature of the present invention is to provide a composition and method for removing iron and iron sulfide solids using a synergistic mixture of IDS or IDS salts and THP or THP salts.
Yet still another feature of the present invention is to provide a composition and method for removing iron and iron sulfide solids using a synergistic mixture of IDS, THP, water soluble surfactants, corrosion inhibitors, defoamers and pH buffering agents.
A feature of the present invention is to provide a composition and method for removing iron and iron sulfide solids with a non-toxic, metal complexing agent.
Another feature of the present invention is to provide a composition and method for removing iron and iron sulfide solids to create water-soluble complexes with iron solids within pipeline networks.
Yet another feature of the present invention is to provide a composition and method for removing iron and iron sulfide solids using environmentally friendly chelating agents.
Yet still another feature of the present invention is to provide a composition and method for removing iron and iron sulfide solids by disrupting the solid matrix of the iron and iron sulfide solids resulting in a dispersion of solids into the liquid phase.
Another feature of the present invention is to provide a composition and method for removing iron and iron sulfide solids by forming soluble complexes of iron that can be removed in the cleaning process.
Another feature of the present invention is to provide a composition and method for removing iron and iron sulfide solids by synergistically combining iron complexing agents.
Additional features and advantages of the invention will be set forth in part in the description which follows, and in part will become apparent from the description, or may be learned by practice of the invention. The features and advantages of the invention may be realized by means of the combinations and steps particularly pointed out in the appended claims.